Distributed Porosity as a Control Parameter for Oxide Thermal Barriers Made by Physical Vapor Deposition

Thermal barrier coatings (TBCs) made by electron-beam physical vapor deposition (EB-PVD) exhibit a thermal conductivity strongly affected by a hierarchy of pores introduced during the deposition process. These pores are in the form of narrow gaps, aligned spheroids, and random spheres at specific sites within the coatings. Models for the effects on thermal conductivity of pores having these shapes and spatial arrangements are taken from the literature and combined with new results to provide descriptors of overall relationships between the relative density and pore morphology of a coating and its thermal conductivity. Correlations between conductivity and elastic modulus are also explored as a means for determining the viability of modulus measurements as a simple-to-use conductivity probe. For the types of pore commonly found in EB-PVD TBCs, there appears to be a tight correlation at typical porosity levels.